Moxon is very slightly shortened 2el yagi. That other thing is effectively weird phased array of two almost halfwave dipoles, and it’s both worse and bigger, and also harder to make because it requires capacitors for gamma match

(Current rabbit hole: Should a HB9CV’s boom be conductive and electrically bonded to its elements?)

Yes it has to be, that’s how you feed its two elements. Boom is at zero electrical potential and forms half of transmission line that goes to gamma matches of both parts of antenna, and you can attach it to perpendicular conductive mast, or extend it for mounting to mast (has to be perpendicular if mast is metal)

Personally, i’d go with 4el yagi if we’re talking portable operation, because boom length is such that you can make it out of plastic tube and hide elements in it when moving around. Or moxon, if size of 4el yagi is prohibitive. Moxon gets you 2db more gain than HB9CV in similar footprint

openhamprep explanation is wrong

When you consider a segment of wire, it has some inductance and capacitance in that small segment, and the wider it is, the lower inductance and higher capacitance are. In other words, both X_L and X_C go down as diameter increases. Electric field lines within antenna are mostly perpendicular to wire everywhere except on ends, where they spread in all directions, which means that there’s some residual capacitance there that needs to be charged each cycle. This is called end effect and the wider wire is, the more of it you get. In fact, the same aspect ratio (length/diameter) gets you the same end effect ratio each time, and it’s usually in range of 0.98-0.95. If there’s insulation, then insulation has lower velocity of propagation as it has higher permittivity than air, and it is in place with highest electric field intensity, and this can also shorten necessary wire length a couple %. The more insulation there is, the more shortened antenna becomes. have a calculator: https://www.translatorscafe.com/unit-converter/en-US/calculator/dipole-antenna/

But wait, there’s more. We can think of antenna as a lossy RLC resonator (sort of), where R is Rrad which for halfwave dipole would be 72 ohms, + loss resistance which is smaller, and neither are changing fast with frequency. What is changing faster is X_L and X_C, and the wider wire is, the smaller both of them are (X_L = -X_C at resonance), and this means that you can go further off frequency and still have acceptable SWR, i.e. antenna made with wider wire has more bandwidth, or if we look at it as resonator, lower Q. For HF this means using masts or wire cages instead of single wire, but for VHF this gets more practical

Resistive part of antenna impedance near resonance depends on physical antenna length, and if antenna is shortened, then how it was done, but for the range we’re here it won’t change much. But also it will depend on height above ground, type of soil, antenna geometry and many other things. 72 ohm is in freespace only

you can consider antenna wire as a transmission line, but it will need to include ground as the other side of transmission line, and then impedance is dependent on wire diameter to height over ground ratio. it’s not very useful except when considering very large and currently uncommon types of antennas (beverage antenna and rhombic antenna, both of which are traveling wave antennas)

this is how antibodies work

it would be about as reliable either way

that’s no problem at all, systems like that are in use

It’s easier to freeze water than to cool rock borehole

you can selfhost an instance from it

this is silicon metal surgical siliconE has density almost equal to water

Could be. Amplifiers are a bit more complicated and there are many things that can limit bandwidth

If we consider groundplane antenna, which should be much better than anything that you can fit on a HT, it might be centered on 145MHz (region 2 band) and it’ll be good for 10MHz for 1:1.5 SWR (140-150) and 17MHz for 1:2 SWR (136.5-153.5) according to some random measurement, first that i found. Outside of these ranges SWR rises rapidly and if you tried to transmit on say 170MHz you might get SWR 1:5, perhaps 1:10 or worse if you’re unlucky. On receive this doesn’t matter too much because these nano- to microwatts of rx power would just bounce back harmlessly with the only effect being that apparent signal strength is lower. But if you tried to transmit then design currents or voltages would be exceeded and something will break, usually final stage of amplifier. This gets rarer than it used to be because some radios can measure SWR and will reduce power in such scenario. This also gets worse the higher transmitted power is

This happens because unlike on HF + 6m, on 2m and up ATUs are not a thing* and all antennas are expected to be matched. So you can use the same radio on GMRS or PMR or what have you and on 2m or 70cm band, but you have to change antennas between these uses. If you want to use all of these on one antenna, then there are special wideband designs like LPDA but this makes sense on a mast and not on handheld radio

* there are tuner designs that work on 2m and up, but you won’t find them in HT, there’s no point, they’re too big, too heavy and too expensive

Even if you tried and made it to work, there might be other incredible problems with things like harmonics or other spurious emissions because filters were not designed to work way out of these frequencies. For example you can try to force Quansheng UV-5K (?) to transmit on 60-ish MHz but most of the power goes out at 2nd and 3rd harmonic, because of the way filters were set up. Narrowband designs are much easier and this is what you’ll see all the time in amateur radio. Wideband and ultrawideband designs are constant source of job security for RF/microwave engineers

You can think of matching units and antennas (and to some degree even feedlines) as filters to some degree, because their bandwidth is not infinite

Note that there’s 25% of fractional bandwidth in there and many antennas won’t work everywhere in that range (and also other elements like power dividers, diplexers etc if part of circuit)

there are also solar xrays, which also ionize ionosphere and are associated with CMEs (regular processes on surface of sun cannot make much xrays, it’s only when high energy particles are smashed back at the surface xrays are emitted. intense magnetic fields are needed for that)

Huh weird. There must be something evil in that pole, it might be a piece of metal or maybe it’s wet or rotting inside. I’d use plastic things to tie it, because natural fibers will remain wet some time after rain, that might degrade performance. (zipties or nylon fishing line or whatever preferably monofilament). I see that bottom is secured too, this is good because in wind antenna could flap around and would stop working if it’s too close to the pole. If twin lead is slightly twisted and under strain (half turn per 30cm or so) then it should flutter less in wind, but you’ve got it spliced and i’m not sure how that would work. This is likely fine as is

J-pole type antennas are effectively monoband. They might work on 3rd harmonic which would be here 70cm band, but most of signal in this case goes up and down that is it’s useless and the signal that goes out horizontally is 6db weaker than what it would be with J-pole for that band. So you can take more precise measurement by zooming in to 130-160MHz or even 140-150MHz, this way you’ll see how low does SWR go at band edges because now you can only see that there is minimum somewhere in the band. I don’t know how much your radio tolerates, but 1:1.5 is generally pretty good. On receive only it might be good also at other frequencies, but dedicated antenna would be likely better

I don’t know if you have calibrated your VNA with cable or not, you can use Smith chart if you do calibrate it with cable but without it, SWR shouldn’t change too hard with any reasonable length of cable (Smith chart rotates once per half wavelength of feedline). This is useful especially if you make your own antennas, but here it’s fine just to make sure that SWR is low

have you calibrated your nanovna? you have to do that after every change of frequency range. you need S11 smith chart, not S21 smith chart (port 2 is not connected). swr and logmag get you the same info in different formats, pick 1

1m away from metal things should be okayish but the more the better. these lights will interfere, if you could at least move them away from the corner it would be an improvement. twin lead cannot be close to metal either (is that sheet metal near bottom of antenna?) needs at least couple cm of distance from it

strictly speaking that’s a slim jim. why does it have a twist in the middle? untwist it, the radiating part (upper approx 1m) should be a smooth transmission line for it to work right (or shorted at both ends)

If you want to preserve the way it’s made, you’d need to resolder the top bar after adjustment. But you also can leave wires on top unconnected

cremieux (real name jordan lasker) is a massive racist https://en.wikipedia.org/wiki/Jordan_Lasker

HF ISM bands as used (NFC things etc) are probably in sub-mW power range, there are regulatory limits on field strength and 27 MHz is additionally limited to 10 mW EIRP. Unless you have curtain that can hear signals from the future i don’t think there’s a lot to listen

No, width is your design parameter. I’ve used 4mm wire because store ran out of 5mm wire, but 3mm would be fine too if you can make it work mechanically. Were it all in air with no plastic, width of both is such that impedances of matching section are close to 300 ohm. Plastic around it lowers impedance and makes wire appear longer. 2m antenna has 220 ohm matching section and it also works. Rectangular connection boxes also work but the ones i could get weren’t as stiff. The way it’s done, bottommost section can be clamped with a regular pipe clamp, it’s harder with a box. Either way 4 or 5mm is not thin on 70cm so impedance of dipole will be probably lower than 5000 ohm, and entire band is covered so it just works

Pick any material you’re comfortable with. Start with 1 wavelength + couple cm of wire, measure out 1/4 and bend it so that 1/4 length point ends up at the bottommost point. Tune by trimming (both arms, lengths of shorter and longer should stay 3:1) and match by moving feedpoint lower or higher (lower is lower impedance). That’s why I’ve made them this way, you can see marks from screw near feedpoint because feedpoint was moved a bit both sides during tuning. By the time trimming gets minimum SWR close to say 420MHz adjust feedpoint to get minimum SWR then alternate between trimming and adjusting feedpoint if necessary. Every mm counts, small trims are better done by filing the wire down instead of cutting it. Plastic needs to stay on during measurement. Keep some 1m of free space (without large metal things) around antenna during measurement

Paging @tasankovasara@sopuli.xyz for logistically efficient antennas

Most of the magnetic flux should be contained in ferrite, and the part that leaks is pointed at the middle of other ferrite so it shouldn’t induce anything. This is fine